On my last several flights in the A350-900ULR, the aircraft can't hold climb speed or a normal climb rate above ~10,000 ft while Live Weather is on. Turning off Live Weather fixes it right away. I haven't seen this in non-INI aircraft, so I'm reporting it here before opening a ticket with Asobo/MSFS.
Build: 1.2.6

Steps to reproduce

1. Load the A350-900ULR at VOHS with Live Weather on (29 Sept 2026, ~12:00 UTC).

2. Depart with TOW: 414.3, ZFW 350.5, fuel 65.2, CI 160, thrust levers in CL.

3. Climb through ~10,000 ft MSL toward FL410.

4. Watch TAT/SAT, speed, and vertical speed.
   

   Workaround

   • Turning off Live Weather makes TAT drop sharply, and performance goes back to normal.

   • Turning Live Weather back on makes TAT go back to a level which is unrealistic for that altitude.
     
     Live weather disabled:
     

Live weather enabled:

Hi,

Are you using any type of 3rd party weather system or default weather?

Thanks!

I have Rex Atmos Core, which theoretically shouldn't impact it since I'm not doing weather injection.

That said, I've experienced this with default weather and Rex Atmos Core.

58 minutes ago, kewtz said:

I have Rex Atmos Core, which theoretically shouldn't impact it since I'm not doing weather injection.

That said, I've experienced this with default weather and Rex Atmos Core.

If you're willing to test, try turning off REX and see if it affects the TAT.

Thanks!

18 hours ago, kewtz said:

I have Rex Atmos Core, which theoretically shouldn't impact it since I'm not doing weather injection.

That said, I've experienced this with default weather and Rex Atmos Core.

If you start up Rex Atmos before fully loading into a flight this is what occurs, and that's even if you don't touch the weather option inside it. That's what causes TAT at ground temps even at high altitudes.